One known method of manufacturing printed circuit boards uses photolithographic techniques to produce desired patterns of conductor structures on an electric insulating substrate, i.e. carrier board. In such photolithographic processes, photosensitive material (photoresist) is exposed to light according to the desired pattern of conductor structures; the photoresistive material is then developed so that metal underneath layers are only accessible in certain areas. Further steps comprise etching the underneath layers, removing the remaining photoresist and possibly depositing additional metal layers either by electroplating or by electroless (chemical) metal deposition. Cleaning and activating steps may also be included. Such known methods are commonly classified into subtractive and additive methods. To produce through-holes or blind holes, mechanical drilling with subsequent copper deposition is used.
More recently, lasers have also been used in the manufacture of printed circuit boards. EP-A-O 164 564, for example, discloses the use of an excimer laser to produce blind holes in a substrate; the process of removing material from a substrate is called laser ablation. EP-A-O 287 843 discloses the removal of nucleation on a carrier board, for example a palladium compound, by a UV laser. The removal of an etch resist layer by a Nd-YAG laser is disclosed in EP-O 469 635. From Research Disclosure RD 32646, published June, 1991, a process for making a printed circuit board is known which starts from a laminate comprising a central layer containing catalyst particles which can activate an electroless plating process and a second layer which does not contain catalyst particles. The second layer is removed in certain areas and holes are created by laser ablation, and finally electroless plating is carried out to metallize the pattern and the walls of the holes.